But on BBC1’s family tree show Who Do You Think You Are? he discovers Peter was killed on his doorstep, in the dead of night, by a British intelligence officer. He then pinned a note to the corpse suggesting it was the IRA.

When the murder took place, Brendan’s father Gerard, who was 10 at the time, and sister Martha, 12, were both asleep. Peter’s wife Annie was the only witness to see “two or three” shadowy figures leave.

On the show screened next week, Brendan discovers his grandmother refused to co-operate with the military inquiry into her husband’s death.

In a letter to them, she said she would not attend a court “conducted by the murderers of my husband.”